The assembly, testing and handling of modern blow out preventer stacks on offshore floaters and drilling rigs is a major consideration in conducting an efficient and safe operation under the dynamic conditions of a marine environment. High day rates for labor and capital investment dictate the adoption of a design for material handling which will reduce installation time so that drilling can be started as soon as feasible.
In order to facilitate operations and enhance safety it is desirable to assemble and test the upper and lower blow out preventer stacks on a test stump prior to the completed unit being moved over the moon pool. Also, in floating vessels, forces due to the roll of the vessel should be minimized as the blow out preventer stacks are quite heavy and the means for moving the assembled blow out preventers into position over the moon pool should not be affected by ship dynamics and should be capable of maintaining a positive control in both forward and reverse directions so that the accelerative forces imparted to such means in the direction of motion due to pitch and roll do not create an uncontrollable runaway situation as a result of the additive effect of energy input in the direction of motion.
The following United States patents generally set forth the state of the art; however, most of them merely disclose various means for moving equipment from various areas of storage to a position over the drilling well (moon pool) of a vessel: U.S. Pat. Nos. 3,031,167; 3,043,255; 3,177,954; 3,189,093; 3,333,562; 3,662,822; 3,699,688; 3,739,736; 3,766,874; and 3,802,209.
None of these patents, however, discloses or suggests the blow out preventer handling system, and the self-aligning connection for the rotary table, of the present invention.